1. Field of the Invention
The present invention relates to an insulating film forming method and its apparatus, and particularly relates to a method for forming a low dielectric insulating film with holes and its apparatus.
2. Description of the Related Art
Against the background of the demand for the high-speed performance and miniaturization of the semiconductor device, the multilayering of the semiconductor device and the wire fining have been developed. However, there is a problem in that a signal propagation velocity becomes low in accordance with the multilayering of the semiconductor device and the wire fining. For example, in the design rule with 0.15 μm or less, there is a possibility that the propagation velocity at which the signal travels through the wire having a multilayer structure will decrease to make it impossible to attain a desired high-speed performance. In order to prevent an increase in a signal delay caused by this fining, it is useful to constrain the dielectric constant of an interlayer insulating film of the wire to be low.
For this reason, the use of various kinds of insulating film forming materials was conventionally reviewed. Among them, attention has been paid to insulating films with a high porosity using a property in which a dielectric constant as a film becomes lower than a dielectric constant native to the material when holes exist in the film.
As the method for forming the insulating film with holes, for example, Unexamined Japanese Patent Publication 2000-277507 and Unexamined Japanese Patent Publication H10-340899 disclose a method in which an insulating film containing a hydrocarbon and the like is formed by, for example, CVD (Chemical Vapor Deposition) and low boiling point ingredients are removed to form holes in an insulating film.
In treatment after forming the insulating film, for example, a heat treatment that heats a substrate on which the insulating film is formed at high temperature. However, the practical insulating film has a relatively high thickness of about 500 nm to 700 nm (about 5000 Å to 7000 Å). For this reason, a temperature gradient is caused in a thickness direction of the insulating film. There was a problem in that the temperature gradient caused deviations in a hole size and a film density from the surface of the insulating film to its interior, making it difficult to form an insulating film with an uniform film characteristic. Moreover, there was a case in which an area with a small porosity was left in the part of the insulating film, so that the dielectric constant of the insulating film did not sufficiently decrease.